EP2419543B1 - Powder for a wire cored with sulfur, cored wire and method for manufacturing a cored wire using same - Google Patents

Description

The invention relates to the field of metallurgy, and more specifically to cored wires by means of which sulfur additions are made in baths of liquid metal, especially steel and metal alloys.

The wire filled with sulfur powder is injected into the liquid steel to improve the machinability of the final steel by promoting the formation of brittle chips that evacuate more quickly during machining parts. Sulfur also reduces the wear of cutting tools due to the lubrication effect provided by the non-metallic inclusions that contain it, and improves the surface condition of these tools. The document JP52101621 describes such a method. The addition by cored wire provides a satisfactory accuracy on the amount of sulfur added, especially if it must be relatively small compared to the total mass of liquid metal concerned.

Such a cored wire is composed of a metal envelope containing a compacted sulfur-based powder. The manufacture of this wire, as for flux-cored son containing other types of additives such as silico-calcium, can typically start with a gravity flow of powdered sulfur on a moving metal strip. The band must have a composition compatible with that of the metal to be additivé. It is made of steel when the sulfur has to be added to a bath of liquid steel. The strip is then welded or folded back on itself by mechanical profiling by means of a roller device, to obtain a cored wire which is then calibrated to the desired diameter. Other processes for preparing cored wire are known, some of which involve extrusion and cold rolling techniques.

The invention applies primarily to son manufactured by mechanical profiling, but it is not a priori excluded to use the powder according to the invention will be described to manufacture filled son by other methods.

The production of the cored wire involves several types of mechanical stresses, including shear stresses. The sulfur powder undergoes various deformations during the manufacture of the wire, and this according to its intrinsic mechanical characteristics. By applying these constraints, the powder is densified cold at various gradients.

The origin and processes of sulfur extraction are very diverse (extraction in the native state, from minerals, petroleum products, etc.). Sulfur exists under different crystallized allotropic varieties, including orthorhombic α and monoclinic β sulfur. The sulfur that makes up the cored wire used in metallurgy, in particular for steel and ferrous alloys, conventionally has a purity greater than 95%, generally greater than 98%, or even 99.5%. A wire filled with sulfur powder conventionally has an outer diameter of 5 to 25 mm and an envelope thickness of 0.1 to 2 mm.

The sulfur powder contained in the cored wire is the result of several grinding operations. This results in a particle size distribution specific to the industrial process for obtaining powders.

• une économie substantielle sur les coûts de fabrication du fil fourré, donc sur son prix d'achat ;
• une économie sur les frais de logistique lors du transport du fil fourré ;
• une économie sur l'espace de stockage des bobines de fil fourré ;
• une meilleure diffusion du matériau contenu dans le fil fourré au sein du métal liquide grâce la présence de fines particules ;
• une limitation de l'ajout de gaz injecté à l'intérieur des bains des métaux liquides pour réaliser l'agitation du bain favorisant la dilution des additifs ;
• une absence d'agent de liantage et/ou de lubrification du matériau d'origine.

For the user, it is interesting that the linear density of the sulfur contained in the cored wire is as high as possible. Indeed, the increase in the linear density of the cored wire brings to the user several technical and economic advantages:

• a substantial saving on the costs of manufacturing the cored wire, therefore on its purchase price;
• a saving on logistics costs when transporting the cored wire;
• saving on the storage space of the cored wire coils;
• a better diffusion of the material contained in the flux-cored wire within the liquid metal by virtue of the presence of fine particles;
• a limitation of the addition of gas injected inside the baths of the liquid metals to effect agitation of the bath promoting the dilution of the additives;
• an absence of binding agent and / or lubrication of the original material.

To date, to the knowledge of the applicant, the optimization of the filling of the cored wire has not been the subject of specific work. Each commercial cored wire therefore has a linear density which is a function of the manufacturing process and the initial physical characteristics of the powders.

The object of the invention is to provide a sulfur-cored wire manufacturing method for optimizing the linear density of the cored wire.

For this purpose, the subject of the invention is a powder for cored wire according to claim 1.

According to particular embodiments, the powder has one or more of the characteristics corresponding to claims 2 to 4.

The invention also relates to a cored wire according to claim 5.

According to one particular embodiment, the cored wire has the characteristics corresponding to claim 6.

The invention also relates to a method according to claim 7.

In a particular embodiment, the method has the features corresponding to claim 8.

As will be understood, the invention is based on a particular constitution of the powder, in that it has a precise particle size distribution, resulting or that can result from a mixture in determined proportions of two defined and differentiated particle size populations , although it is not strictly excluded that they may sometimes have some recovery.

The advantage of the invention is to introduce a maximum of powder mass within this flux-cored wire, with constant section. This makes it possible to reduce the intergranular porosity of the final compact mixture.

A granular assembly may be characterized by its ability to rearrange due to flow or vibration. This set rearranges more or less well, depending on the physical characteristics of the particles and the particle bed: the particle size, the true density of the powder material, the morphology of the particles, the compressibility of the granular set, the particle size distribution.

The quality of the granular stack after flow and / or vibration influences the filling level of the cored wire. The granular rearrangement is more or less random. It depends mainly on the morphology, size and surface appearance of the particles. The innovation provided by the invention consists of optimizing and improving this stack in order to obtain the best level of filling possible while maintaining the final mechanical characteristics of the wire. It is also necessary to take into account the intrinsic properties of the filling material, which make it that it will react in a particular way to the stresses to which it will be subjected during the manufacture of the wire, in particular during the closing and welding steps or profiling of the envelope. For this reason in particular, the problem of optimizing the linear density of the final cored wire can not have a single solution, valid whatever the filling material. This optimization must be fine-tuned according to the exact nature of the material.

By a succession of experiments and different analyzes of the results obtained, the inventors have determined what they think is the best particle size distribution for optimal filling of the flux-cored wire with sulfur particles. This particle size distribution develops a dense stack, while providing an easy flow of the powder bed during the deposition of the powder on the metal strip during the manufacture of the wire. The flowability of this granular set is characterized by the Hausner index and the compressibility index.

The compressibility of a granular medium is related to the flow properties, because it is representative of the intergranular forces and therefore, indirectly of the cohesion of the medium. The higher the inter-particle forces, the more the medium will be able to compress if the shocks applied are sufficiently energetic.

où :

• ρ_tassée est la masse volumique apparente tassée,
• ρ_aérée est la masse volumique apparente non tassée,

The compressibility index is determined by the ratio of the densities aerated and packed: $$\mathrm{Compressibility}=\left({\mathrm{\rho }}_{\mathrm{packed}}-{\mathrm{\rho }}_{\mathrm{airy}}\right)/{\mathrm{\rho }}_{\mathrm{packed}}$$

or :

• ρ _packed is the bulk density packed,
• ρ _aerated is the uncapped bulk density,

The Hausner I _H index, always greater than 1, increases when the flow velocity decreases, so when inter-particle friction increases. It is sensitive to the morphology, appearance, size, density of the powder and residual moisture. It is defined by: $${\mathrm{I}}_{\mathrm{H}}={\mathrm{\rho }}_{\mathrm{packed}}/{\mathrm{\rho }}_{\mathrm{airy}}$$

During a random granular rearrangement, a reduction in intergranular porosity results after gravity flow.

• 1 µm ≤ d10 ≤ 340 µm ;
• 200 µm ≤ d50 ≤ 2000 µm ;
• 500 µm ≤ d90 ≤ 2900 µm.

The particle size populations composing the resulting mixture of the invention are defined as indicated below:

• 1 μm ≤ d10 ≤ 340 μm;
• 200 μm ≤ d50 ≤ 2000 μm;
• 500 μm ≤ d90 ≤ 2900 μm.

• 20 µm ≤ d10 ≤ 300 µm ;
• 800 µm ≤ d50 ≤ 1900 µm ;
• 2000 µm ≤ d90 ≤ 2700 µm.

A preferred variant of this mixture is defined by:

• 20 μm ≤ d10 ≤ 300 μm;
• 800 μm ≤ d50 ≤ 1900 μm;
• 2000 μm ≤ d90 ≤ 2700 μm.

The density in the packed state resulting from this granular assembly is of the order of 1.0 to 1.70 g / cm ³ . The morphology of the sulfur particles can be spherical as well as rounded, of the needle, fiber or polyhedron type. The compaction rate within this cored wire is usually of the order of 75 to 80%, whereas in the invention a compaction rate of at least 85% is achieved.

• l'indice d10 définit le diamètre équivalent pour lequel la valeur de la distribution cumulée est de 10% en masse ;
• l'indice d50 définit le diamètre équivalent pour lequel la valeur de la distribution cumulée est de 50% en masse ;
• l'indice d90 définit le diamètre équivalent pour lequel la valeur de la distribution cumulée est de 90% en masse.

Preferably, this powder is obtained by an optimized combination of several distinct particle size populations of sulfur particles of purity of at least 95%, preferably greater than 98%, whose sizes are in the range [0 - 5000 μm] applied to the cored wire. This combination is a homogeneous mixture of various precise mass proportions of each population, obtained conventionally using a rotating bowl granular stirring device. The particle size distributions of the populations of the invention are defined by the indices d10, d50, d90.

• the index d10 defines the equivalent diameter for which the value of the cumulative distribution is 10% by mass;
• the index d50 defines the equivalent diameter for which the value of the cumulative distribution is 50% by mass;
• the index d90 defines the equivalent diameter for which the value of the cumulative distribution is 90% by mass.

From mixtures of these particle size populations, a fill level increase of 10 to 70% of the linear density is typically obtained with respect to a wire of the same diameter using the same shell and manufactured under the same conditions using of any one of these populations. The compaction rate of these son filled with sulfur after the manufacture of the wire is, according to the invention, greater than or equal to 85% to achieve an optimal linear density.

• Population 1 :
  • 350 µm ≤ d10 ≤ 1400 µm
  • 650 µm ≤ d50 ≤ 2200 µm
  • 1000 µm ≤ d90 ≤ 3000 µm
• Population 2:
  • 1 µm ≤ d10 ≤ 250 µm
  • 50 µm ≤ d50 ≤ 500 µm
  • 100 µm ≤ d90 ≤ 800 µm

The particle size populations invented by the inventors according to a preferred version of the invention, in which two populations 1 and 2 are used, are described as follows:

• Population 1:
  • 350 μm ≤ d10 ≤ 1400 μm
  • 650 μm ≤ d50 ≤ 2200 μm
  • 1000 μm ≤ d90 ≤ 3000 μm
• Population 2:
  • 1 μm ≤ d10 ≤ 250 μm
  • 50 μm ≤ d50 ≤ 500 μm
  • 100 μm ≤ d90 ≤ 800 μm

The experimental protocol applied in the laboratory is initially to mix populations with a given particle size distribution in precise mass proportions. Then, the physical characteristics of the different mixtures, such as grain size distribution and density, are measured. These data make it possible to set up a behavioral and phenomenological modeling of the system.

The models obtained indicate associations of ideal mass and particle size proportions. A granular selection is then made upstream in order to distribute the granulometric classes artfully. The optimal particle size distribution is ultimately composed of an association of several size classes.

These mixtures tested on the industrial process for manufacturing flux cored wire confirm the modeling phase of the experiment in the laboratory. For example, the optimum mixture is composed of 65 to 75% by weight of the population 1, homogeneously mixed with 25 to 35% by weight of the population 2. A mixture is considered optimal when it has the properties of flow and the highest compacities.

These mixtures are created using a standard commercial type rotating bowl mixer. The internal walls of the mixer are composed of buckets judiciously fixed to limit the granular heterogeneity. They allow the materials to be brewed delicately without modification sensitive particle size of the powder bed. The homogeneity of the mixture is ensured for a brewing time of 1 to 10 minutes.

The compaction rate of the powders within the cored wire is determined by the physical characterization of several representative samples by the mercury intrusion porosimetry technique. This destructive analysis makes it possible to measure the pore size distribution of the intra- and intergranular open porosity. In parallel, the theoretical density of a powder material is measured by helium pycnometry. This thus makes it possible to evaluate the degree of compaction and to evaluate the degree of porosity of the granular assembly within the cored wire.

The cored wire is technically characterized in particular by its linear density, depending on its degree of filling. This degree of filling is a result of the density of the pulverulent or granular population that composes it. The traditional steel-filled sulfur-filled wire, with an outer diameter of between 13 and 14 mm, has a linear density in the range [180 g / m - 205 g / m]. The usual particle size distribution of the powder it contains is in the range [0 μm - 5000 μm].

Examples of known reference sulfur-filled son and sulfur-filled son according to the invention will now be described which will demonstrate the advantages of the invention. These yarns were manufactured by the method preferred in the invention of depositing the powder on a metal strip, welding or folding said strip on itself to form the wire and profiling the wire to bring it to its nominal diameter.

Reference Example 1: Manufacture of a Standard and Known Sulfur Powder Coated Wire with an External Diameter of 13.1 mm and a Strap of 0.39 mm Thickness

• Pureté de la population : S = 99,95% ;
• Masse volumique pycnométrique : 2,02 g/cm³
• Masse volumique tassée : 1,18 g/cm³ ;
• Masse volumique aérée : 1,09 g/cm³ ;
• Indice de compressibilité : 7,62% ;
• Indice d'Hausner : 1,08 ;
• d10 compris entre 0,800 et 1,000 mm ;
• d50 compris entre 1,600 et 2,000 mm ;
• d90 compris entre 2,000 et 2,360 mm.

For a population A whose particle size distribution and characteristics are given below: Table 1: Particle size distribution of population A according to ASTM E11-01 Size class (mm) Percentage <0.045 0.2 0.045 - 0.075 0.2 0.075 - 0.100 0.2 0.100 - 0.150 0.3 0.150 - 0.200 0.2 0.200 - 0.250 0.2 0.250 - 0.300 0.1 0.300 - 0.425 0.5 0.425 - 0.500 0.1 0.500 - 0.630 1.3 0.630 - 0.800 3.4 0.800 - 1,000 4.3 1,000 - 1,250 10.0 1,250 - 1,400 8.6 1,400 - 1,600 0.1 1,600 - 2,000 34.9 2,000 - 2,360 28.6 2,360 - 2,800 6.3 2,800 - 3,350 0.5

• Purity of the population: S = 99.95%;
• Pyknometric density: 2.02 g / cm ³
• Packed density: 1.18 g / cm ³ ;
• Aerated density: 1.09 g / cm ³ ;
• Compressibility index: 7.62%;
• Hausner index: 1.08;
• d10 between 0.800 and 1.000 mm;
• d50 between 1,600 and 2,000 mm;
• d90 between 2,000 and 2,360 mm.

The linear density developed within the cored wire made from this population A only, whose d10 is too high to comply with the invention, is 189 g / m with a compaction rate of 78%.

Example 2, corresponding to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 13.1 mm with a 0.39 mm thick strip

• Pureté de la population : S = 99,95% ;
• Masse volumique pycnométrique : 2,02 g/cm³ ;
• Masse volumique tassée : 1,13 g/cm³ ;
• Masse volumique aérée : 0.90 g/cm³ ;
• Indice de compressibilité : 20,35% ;
• Indice d'Hausner : 1,25 ;
• d10 compris entre 0,045 et 0,075 mm ;
• d50 compris entre 0,200 et 0,250 mm ;
• d90 compris entre 0,300 et 0,425 mm.

Another population B of powder is used, whose grain size distribution and characteristics are given below: Table 2: Particle size distribution of population B according to ASTM E11-01. Size class (mm) Percentage <0.045 3.8 0.045 - 0.075 7.8 0.075 - 0.100 9.9 0.100 - 0.150 12.9 0.150 - 0.200 14.7 0.200 - 0.250 12.9 0.250 - 0.300 10.9 0.300 - 0.425 23.1 0.425 - 0.500 3.6 0.500 - 0.630 0.3 0.630 - 0.800 0.1 0.800 - 1,000 0.1 1,000 - 1,250 0.1 1,250 - 1,400 0.0 1,400 - 1,600 0.0 1,600 - 2,000 0.0 2,000 - 2,360 0.0 2,360 - 2,800 0.0 2,800 - 3,350 0.0

• Purity of the population: S = 99.95%;
• Pyknometric density: 2.02 g / cm ³ ;
• Packed density: 1.13 g / cm ³ ;
• Aerated density: 0.90 g / cm ³ ;
• Compressibility index: 20.35%;
• Hausner index: 1.25;
• d10 between 0.045 and 0.075 mm;
• d50 between 0.200 and 0.250 mm;
• d90 between 0.300 and 0.425 mm.

As the flow indices of this powder are mediocre (high compressibility index and Hausner index), this powder alone, whose d90 is too low for it to conform to the invention, does not make it possible to obtain cored wire of regular linear density under normal manufacturing conditions.

• Masse volumique pycnométrique : 2,02 g/cm³ ;
• Masse volumique tassée : 1,47 g/cm³ ;
• Masse volumique aérée : 1,25 g/cm³ ;
• Indice de compressibilité : 14,96% ;
• Indice d'Hausner : 1,17 ;
• d10 compris entre 0,100 et 0,150 mm ;
• d50 compris entre 1,250 et 1,400 mm ;
• d90 compris entre 2,000 et 2,360 mm.

For a mixture forming a population C consisting of 70% by mass of batch A and 30% by mass of batch B, the particle size distribution and characteristics of which are given below: Table n ° 3: Granulometric distribution of the population C according to the standard ASTM E11-01 Size class (mm) Percentage <0.045 0.0 0.045 - 0.075 2.5 0.075 - 0.100 2.9 0.100 - 0.150 4.8 0.150 - 0.200 5.2 0.200 - 0.250 4.2 0.250 - 0.300 3.6 0.300 - 0.425 7.5 0.425 - 0.500 2.2 0.500 - 0.630 2.3 0.630 - 0.800 3.3 0.800 - 1,000 3.2 1,000 - 1,250 8.0 1,250 - 1,400 1.2 1,400 - 1,600 2.9 1,600 - 2,000 23.2 2,000 - 2,360 18.4 2,360 - 2,800 4.4 2,800 - 3,350 0.2

• Pyknometric density: 2.02 g / cm ³ ;
• Packed density: 1.47 g / cm ³ ;
• Aerated density: 1.25 g / cm ³ ;
• Compressibility index: 14.96%;
• Hausner index: 1.17;
• d10 between 0.100 and 0.150 mm;
• d50 between 1.250 and 1.400 mm;
• d90 between 2,000 and 2,360 mm.

A yarn with a linear density of 237 g / m and a compaction ratio of 88% is obtained. The linear density is 25% greater than that of a similar wire of the same external diameter 13.1 mm and a strip thickness of 0.39 mm manufactured under the same conditions from the only population A, although this population A was mixed with the population B which, taken separately, would not lead to satisfactory results because of its poor flowability.

Example 3, corresponding to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 13.1 mm with a 0.39 mm thick strip

• Pureté de la population : S = 99,95% ;
• Masse volumique pycnométrique : 2,02 g/cm³ ;
• Masse volumique tassée : 1,14 g/cm³ ;
• Masse volumique aérée : 1,03 g/cm³ ;
• Indice de compressibilité : 9,64% ;
• Indice d'Hausner : 1,10
• d10 compris entre 0,800 et 1,000 mm ;
• d50 compris entre 1,600 et 2,000 mm ;
• d90 compris entre 2,360 et 2,800 mm.

A sulfur powder constitutes a population D and has the particle size distribution and the following characteristics: Table n ° 4: Granulometric distribution of the population D according to the standard ASTM E11-01 Size class (mm) Percentage <0.045 0.1 0.045 - 0.075 0.2 0.075 - 0.100 0.2 0.100 - 0.150 0.2 0.150 - 0.200 0.2 0.200 - 0.250 0.2 0.250 - 0.300 0.2 0.300 - 0.425 0.9 0.425 - 0.500 0.9 0.500 - 0.630 2.3 0.630 - 0.800 4.3 0.800 - 1,000 6.6 1,000 - 1,250 12.1 1,250 - 1,400 7.2 1,400 - 1,600 0.5 1,600 - 2,000 31.6 2,000 - 2,360 20.1 2,360 - 2,800 11.9 2,800 - 3,350 0.2

• Purity of the population: S = 99.95%;
• Pyknometric density: 2.02 g / cm ³ ;
• Packed density: 1.14 g / cm ³ ;
• Aerated density: 1.03 g / cm ³ ;
• Compressibility index: 9.64%;
• Hausner Index: 1.10
• d10 between 0.800 and 1.000 mm;
• d50 between 1,600 and 2,000 mm;
• d90 between 2,360 and 2,800 mm.

The use of this D population alone, whose d10 is higher than that required by the invention, makes it possible to obtain a cored wire of external diameter 13.1 mm with a strip of 0.39 mm whose linear density is 181 g / m with a compaction rate of 76%.

• Masse volumique pycnométrique : 2,02 g/cm³ ;
• Masse volumique tassée : 1,43 g/cm³ ;
• Masse volumique aérée : 1,16 g/cm³ ;
• Indice de compressibilité : 18,80% ;
• Indice d'Hausner : 1,23
• d10 compris entre 0,075 et 0,100 mm ;
• d50 compris entre 1,600 et 2,000 mm ;
• d90 compris entre 2,360 et 2,800 mm

A mixture forming a population E consisting of 60% by weight of the population D and 40% by weight of the population B is produced, and which has the particle size distribution and the following characteristics: Table n ° 5: Granulometric distribution of the population E according to the standard ASTM E11-01 Size class (mm) Percentage <0.045 3.8 0.045 - 0.075 5.5 0.075 - 0.100 3.5 0.100 - 0.150 5.3 0.150 - 0.200 4.7 0.200 - 0.250 3.6 0.250 - 0.300 3.4 0.300 - 0.425 5.8 0.425 - 0.500 0.4 0.500 - 0.630 1.3 0.630 - 0.800 0.7 0.800 - 1,000 2.5 1,000 - 1,250 2.8 1,250 - 1,400 2.6 1,400 - 1,600 0.2 1,600 - 2,000 17.7 2,000 - 2,360 24.9 2,360 - 2,800 11.0 2,800 - 3,350 0.1

• Pyknometric density: 2.02 g / cm ³ ;
• Packed density: 1.43 g / cm ³ ;
• Aerated density: 1.16 g / cm ³ ;
• Compressibility index: 18.80%;
• Hausner Index: 1.23
• d10 between 0.075 and 0.100 mm;
• d50 between 1,600 and 2,000 mm;
• d90 between 2,360 and 2,800 mm

The use of this population E makes it possible to obtain a cored wire having a linear density equal to 225 g / m, 24% higher than that obtained with the population D alone and a compaction ratio equal to 86%. Here again, the mixture of the population D with the population B in the given proportions made it possible to obtain a cored wire of 13.1 mm with a strip of 0.39 mm manufactured under the same conditions, better characteristics than this one. that the only use of the population D would have allowed.

It should be noted, however, that the compactness and the linear density of this cored wire are slightly inferior to those of the wire of Example 2. This is attributable to the fact that the d90 of the population E is higher than that of the population C, and does not necessarily fall within the preferred range of the invention.

Reference Example 4: manufacture of a cored wire of sulfur powder with an external diameter of 9.2 mm and a strip thickness of 0.20 mm

• Pureté de la population : S = 99,95% ;
• Masse volumique pycnométrique : 2,02 g/cm³ ;
• Masse volumique tassée : 1,14 g/cm³ ;
• Masse volumique aérée : 1,01 g/cm³ ;
• Indice de compressibilité : 11,40%
• Indice d'Hausner : 1,13 ;
• d10 compris entre 0,500 et 0,630 mm ;
• d50 compris entre 1,000 et 1,250 mm ;
• d90 compris entre 1,600 et 2,000 mm.

A sulfur powder constitutes a population F whose particle size distribution and characteristics are as follows: Table 6: Granulometric distribution of the F population according to ASTM E11-01 Size class (mm) Percentage <0.045 0.0 0.045 - 0.075 0.0 0.075 - 0.100 0.0 0.100 - 0.150 0.1 0.150 - 0.200 0.1 0.200 - 0.250 0.7 0.250 - 0.300 1.4 0.300 - 0.425 3.8 0.425 - 0.500 3.0 0.500 - 0.630 6.2 0.630 - 0.800 10.1 0.800 - 1,000 13.0 1,000 - 1,250 20.5 1,250 - 1,400 10.0 1,400 - 1,600 9.4 1,600 - 2,000 20.7 > 2,000 1.0

• Purity of the population: S = 99.95%;
• Pyknometric density: 2.02 g / cm ³ ;
• Packed density: 1.14 g / cm ³ ;
• Aerated density: 1.01 g / cm ³ ;
• Compressibility index: 11.40%
• Hausner's index: 1.13;
• d10 between 0.500 and 0.630 mm;
• d50 between 1,000 and 1,250 mm;
• d90 between 1,600 and 2,000 mm.

The use of this population F alone, whose d10 is higher than that required by the invention, makes it possible to obtain a cored wire 9.2 mm in diameter with a strip thickness of 0.20 mm whose mass linear is 82 g / m with a compaction rate of 75%.

Example 5 according to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 9.2 mm and a strip thickness of 0.20 mm

A mixture consisting of 70% by weight of the population A and 30% by weight of the population B is made according to the population C described in Example 2.

The use of this population C to manufacture a cored wire of external diameter of 9.2 mm with a strip thickness of 0.20 mm as in Reference Example 4 and under the same conditions, makes it possible to obtain a wire having a linear density of 109 g / m, which is 29% higher than that of reference example 4 made from the only population F, and a compaction rate of 89%.

Claims (8)

1. Powder which is for a flux-cored wire intended to become alloyed with a molten metal bath and which is formed by particles composed with at least 95% of sulphur, characterised in that its granulometric population is defined by:

   - 1 µm ≤ d10 ≤ 340 µm;

   - 200 µm ≤ d50 ≤ 2000 µm;

   - 500 µm ≤ d90 ≤ 2900 µm;

   d10, d50 and d90 being the equivalent diameters of the particles for which the values of the cumulative distributions are 10, 50 and 90% by mass, respectively.
2. Powder according to claim 1, characterised in that its granulometric population is defined by:

   - 20 µm ≤ d10 ≤ 300 µm;

   - 800 µm ≤ d50 ≤ 1900 µm;

   - 2000 µm ≤ d90 ≤ 2700 µm.
3. Powder according to claim 1 or claim 2, characterised in that it results from the homogeneous admixture of two granulometric populations 1 and 2, granulometric population 1 constituting between 50 and 90% by mass of the admixture and population 2 constituting between 10 and 50% by mass of the admixture, the populations being defined by:

   Population 1:

   - 350 µm ≤ d10 ≤ 1400 µm ;

   - 650 µm ≤ d50 ≤ 2200 µm ;

   - 1000 µm ≤ d90 ≤ 3000 µm ;

   Population 2:

   - 1 µm ≤ d10 ≤ 250 µm ;

   - 50 µm ≤ d50 ≤ 500 µm;

   - 100 µm ≤ d90 ≤ 800 µm.
4. Powder according to claim 3, characterised in that population 1 constitutes from 65 to 75% by mass of the admixture and population 2 constitutes from 25 to 35% by mass of the admixture.
5. Sulphur-based flux-cored wire intended for alloying with a metal bath, characterised in that it contains a powder according to any one of claims 1 to 4.
6. Sulphur-based flux-cored wire according to claim 5, characterised in that the compaction rate of said powder within the wire is greater than or equal to 85%.
7. Method for producing a sulphur-based flux-cored wire for alloying with molten metal baths, characterised in that it comprises the following steps of:

   - preparing a powder according to any one of claims 1 to 4;

   - dispensing the powder by gravitational force onto a metal strip;

   - welding or mechanically folding the strip on itself in order to form the wire and profiling the wire to the selected diameter.
8. Method according to claim 7, characterised in that the powder compaction rate of the obtained wire is greater than or equal to 85%.